Automatic traffic control system



Aug. 9,l 1938.

F.. VON OPEL AUTOMATIC TRAFFIC CONTROL Filed June 29, 1934 SYSTEM 4 Sheets-Sheet 1 mg.. 9 m38; y FQ VON OPEL 2,126,432

AUTOMATIC TRAFFIC CONTROL SYSTEM Filed June29, 1934 4 Sheets-Sheet 2 Aug. 9, 1 938. F. voN OPEL I 2,126,432

AUTOIATIC TRAFFIC CONTROVL SYSTEM Filed .June 29, 1934 `4 sheets-sheet :s

TIME OLA Y @ELA YJ illllllf Aug. 9, 1938. F. VON OPEL AUTOMATIC TRAFFIC CONTROL SYSTEM Filed June 29, 1934 4 Sheets-Sheet 4 470,5 a wwvwwwfamw Patented 1938 UNITED STATES AUTOMATIC TRAFFIC CONTROL SYSTERIk Fritz von Opel, Berlin-Charlottenburg, Germany Application June 2s, 1934. serial No. 733,113

. In Germany July 8, 1933 s claims. A (cigni-,337)

said co-pending application, I have provided a sig'- c nailing device, normally a lamp displaying green light for proceed, red light for stop, and yellow light for caution. The signalling device or lamp is operated by a motor and a switching. drum. Vehicle-operated controls are. provided in the streets of the crossing, and variable resistances are connected to the motor for increasing and decreasing its speed. The speed increasing means is operated by the control `in the blocked street, and the speed decreasing means is operated by the control in the free street.

In such a system, the durations of the periods,

for which a street is blocked, and for which it is free, are functions both of the number of vehicles waiting in the blocked street, and 'of the number of vehicles moving in the free street. Between a variablel upper and a variable lower limit for which the system is adjusted, the

blocked and free periods vary in proportionto the density of the tra'ic. As the vehicles waiting in the blocked street, through the medium of the vehicle-actuated control, operate the speed increasing means of the motor, they cause a shortening of the blocked period, and, as the vehicles moving in the free street similarly operate the speed decreasing means of the motor, they causea lengthening of the free period.

In the system referred to, the operation is principally performed by mechanical means such as step-by-step rotary switches for effecting the speed increase and decrease. The object of my present invention is to dispense with all rotary or constantly moving mechanical means and to re- 'place them by electrical means. In this manner, the inevitable slack, inertia forces, resistance, etc.,A of such step-by-step switch gear are eliminated.

It is understood, in the present description and claims, that the expression "street crossing includes any intersection of traic lines and is not limited to streets. ForA instance, if such lines intersect in a square, this is not exactly a street crossing but my system may be used in such and other cases as well as for street crossings proper.

Every two of the vehicle-actuated controls are related, i. e., one of them is in a free street while the street' in which the other control is positioned, is blocked, and vice versa. A circuit is provided per control, with means operated by its control for making and breaking thc circuit, and each circuit includes an electrical condenser.

A third electrical condenser operates the signalling .device and is operated, in its turn, .by means under the influencel of the relative condition, for instance. the voltage difference of the condensers, in the two mst-mentioned electrical units. y

In the accompanying drawings, a system embodying my invention is illustrated diagrammatically by way of example.

In the drawings Fig. 1 is aV diagram of the connections, switches,

etc., of the system,

Fig. 1c isa circuit diagram for a street crossing showing the controls and the trafiic signal device,

Fig. 1b is a side view of the switch street operable by the vehicles.

Fig. 1c is a top view showing the cam operated switches and the operator therefor,

Fig. 1d is an end view, of the operator and its circuit Afor the switches of Fig. lc,

Fig. 1e is an across the line diagram of Fig. l, and

Fig. 2 shows the periods during which the several switches of the system are open and closed while the system performs a cycle from yellow over green and red back to.ye1low.

Referring now to the drawings, and first to Fig. l, two correlated vehicle-actuated.' controls are shown at i and 2. The arrangement and the design of such controls are shown in Fig. 1b in which a switch arm IVM is pivoted at |15 and has a contact H2 cooperating with the contact the letter F. The switching means of the two controls are connected, at one terminal, to the negative terminal 3 of a battery 90. The other terminal of control i is. connected to the positive 4 terminal 9 by a circuit 4 which includes the coil of a relay 5, and a manually operated switch i in parallel with a switch 6 which is operated by a switch drum, as will be described below. The other terminal of control 2 is connected to the positive terminal 9 by a circuit Ill which includes the coil of another relay Il and switches 6 and 1. Both circuits are connected to a safety fuse 8 which in turn is connected to the positive tcrmi. nal 9 of battery 90. i i

The relays 5 and Ii operate contacts I2 and i3 which are of the continuity-preserving type, i. e., they make contact for a period which is independent of the period during which the relays attract their armatures. When attracted by The controls are simply shown as `tioned, is free at the same time, as indicated by its relay 5, the continuity-preserving contact I2 closes the following circuit: Battery I4, wire I5, wire I5', condenser I6, wire I5", contact I2, wire I8', resistance'il, and wire I8. The circuit closed by the contact I3 is as follows: Battery I4, wire I5, wire I9, condenser 28, wire I9', contact I3, wire 22', resistance 2|, and wire 22.

The wires I8' and 22 are connected, by wires 21 and 26, respectively, to the contacts 23h and 23a of a switch 23 which is also controlled by the switch drum referred to. A resistance 24 is connected to the switching member of switch 23 at one end, andto the wires I8 and 22 at its other end, by wire 25. By means of the switch 23, this resistance can be connected in parallel to the resistance I1 or to the resistance 2|.

The condensers I6 and 20 are connected in series in the grid circuit as a valve 38 hereinafter described and are charged from battery |4 as often as the contacts I2 and I3 are closed by vehicle responsive impulses received from the controls I, 2 in the blocked and free streets. The difference of the voltages in the two condensers I6 and 20 resulting from the charging thereof by these impulses is transferred to the thermionic valve 38 from contacts I2 and I3 by the following connections: Contact I2, wire 28, contacts 30a and 3Ib. The contacts 30a and 3Ib are parts of throw-over switches 30 and 3l. respectively, whose other contacts 30h and 3Ia are connected to contact I3 by wire 29. Throw-over switch 30 is connected to a grid battery 33 by wire 32 and the battery 33 is, by wire 32', connected to a contact 34a of a throw-over switch 34 whose switching member is connected to the grid 31 of valve 38 through a wire 35 and a high-ohmic resistance 36. The other contact 34b of this throw-over switch is connected to a potentiometer 42 by a movable' tap. Energy is supplied to the potentiometer 42 from a battery 44. The switching member of throw-over switch 3l is connected to the heating wire 40 of valve 38 by a wire 39. The potentiometer 42 is connected directly to the wire 39, and the battery 44 is connected to the wire 39 by a manually operated switch 43. Wires 35 and 39, and through them the grid 31 and the cathode of the valve 38, are connected to each other through a condenser 4I, the third condenser hereinbefore mentioned for receiving the voltage dilerence of condensers I6, 28..

The series connection of the condensers I6 and 20 may be traced as follows through a complete circuit. 'I'he electric current from the condenser ,Ii passes through the wire 28 to the contact 30a, to the battery 33, contact 34a, wire 34, resistance 36, to the grid 31 of the valve 38. From this point the circuit is traced from the cathode of the valve 38 over the wire 49 to the switch 3i and then to the contact 3Ia,` wire 29 to the condenser 20 and from there back to the condenser I6. In Fig. Ie the positions illustrated are those when a green light is showing. When a red light is showing the switches 30 and 3| are connected by means of the contacts 30h and Bib. The switch 34 remains in the position as illustrated. The circuit is thus traced as follows. From condenser I6 the current traverses the wire 28 to the contact 3Ib then over the wire 4|! to the cathode and from there to the grid 31 and through resistance 36, wire 34, contact 34a, through the battery 33, switch. 30 to the contact 30h and over the wire 29 to the condenser 20 and then back to the condenser I6.

A wire 41 leads from the wire 39 to the switching member of a switch 49, the contact 49h of switch 49 is connected to the arm of a switch 48, with contacts 48a and 48h. 'Ihe coni-121, a

formity with the position of switches 3|, 49, and

48, either the resistance 45 is connected in parallel to condenser 20, or the resistance 46 is connected in parallel to condenser I6.

The thermionic valve 38 acts as the variable resistance in a trigger circuit which includes a condenser 50, a relay 52 and a glow tube 5I in series with the relay 52 and in which the condenser is adapted to discharge through the tube when the voltage reaches a certain value. The circuit of glow tube 5I is supplied with current from a network through wires 10 and 1I, and a device 53 for connecting the system to a network. A switch 6I which is operated by the above said switch drurn, and a manually operated switch 62, are connected to the wire 1I. A wire 54, with a high-ohmic resistance 55, and a wire 56, supply the circuit of glow tube 5I. The wire 56 is connected to the contact 49a of switch 49 by a wire A switch 51 has contacts 51a and 51D which are connected to wire 56 through resistances 58 and 59. Both resistances are variable. The circuit of the glow tube 5I is supplied either through resistance 58 or 59-in accordance with the position of the switching member 51 to the contacts 51a, 51h-or. if the switch 5'I is open, and switch 49 closes contact 49a, through wires 60, 41, and 39.

When the relay 52 is excited. it closes a switch 63 which is connected to the negative terminal of a battery 12. The positive terminal of the battery 12 is connected to the coil of an electromagnet 64. The magnet 64 controls a suitable driving means, for instance, a paWLand-ratchet mechanism which advances the switch drum. The mechanism and the switch drum are illustrated in Fig. 1b in which the mechanism is operated by a solenoid or magnet 64 in a circuit including the battery 12, switch arm 63 and coil '52 of a contact cooperating with the switch arm 63. The switching drum controls the sequence of the signals displayed by the yellow lamp 61, the red lamp 68, and the green lamp 89, through switches 65 and 66, with contacts a and 6512, and 66a and 66h, respectively, by which the lamps are connected to the terminals of an alternating-current system.

Switches 1, 43, and 'i2 which, as mentioned, are operated manually while all other switches and contacts, except relay contacts, are controlled by the switching drum through the paWl-andratchet mechanism and magnet 64, are permanently closed, as shown in the lowermost eld of Fig. 2 where the heavy black line extends throughout the diagram. Consider now the green column. At the'commencement of the green period, witch 23 closes contact 23a which is connected to resistance 2|. Switch 3D closes contact 30a and connects wire 28 to battery 32. Switch 3| closes contact 3io. and c )nnects wires 29 and 39. Switch 34 closes contacts 34a and connects the grid 31 of valve 38 to the battery 33.

Switch 49 closes contact 49h and conto the average timea vehicle requires for passing switches s m the circuit or battery sn, and si in the supply wire 1l, are closed. It has already been mentioned that the manually operatedv switches 1, S2 and 43 arev also closed. 'I'he street in which the control i is positioned, is blocked (B), and the street in which control 2 is positioned 'I'he green signal is displayed for increasing counter-voltage of the condenser. The

vehicles arriving at the control in the blocked street atB, therefore produce an effect following a logarithmic law. The condenser i6 corresponds to the blocked street and, as shown by the diagram, the switch 23 closes contact 23h while thestreet is blocked by red light.

The condenser 20 corresponds to the i'ree street. When control 2 (F) is operated by a vehicle moving in the free street, contact I3 is closed by me excited relay Ii, and the switch 23, as described, makes contact at 23a. Resistance 24 is connected inparallel to resistance 2| and reduces the eilect of resistance 2l. By making the resistance 24 variable, variationsof the distance oi the control 2 in the iree street from the crossing may be taken into consideration when the controls are arranged. This consideration of variations, how ever, is only required for the free street.

'I'he condenser 2d is also charged by a logarithniic law, but its ratey of charging ismore rapid tor a given number of impulses, on account of the parallel connectionoit resistance 2d. The diier.- ence ci the voltages between the condensers iii,

it is a function of the ratio of operations of con' tacts l2 and i3, andconsequently to the relative trame density in the blocked and in the free street. This voltage diierence, when the positions of the switches are as described, is connected between the grid 3l, and the heating Wire du, oi valve 3d. At the same time, the resistance d5 is connected in parallel to the condenser iii of the free street F. The resistance it permits a continuous discharge oil the condenser to. By this continuous discharge oi the condenser 2li for the free street, the tact is considered that the vehicles which move'past the control 2 in the free street, the crossing after a tew seconds, and

therefore the influence of these vehicles must disappear aiter the free period has elapsed. The resistance 45 is so designed that the maximum partial, i. e., initial. charge oi the condenser 2li,l

is discharged during a time .which corresponds the crossing.

The resistance of valve 38 and the charging time ot condenser MI is determined by the voltage diil'erence of condensers lo and owhich may be high or low, pontive or' negative. I'he voltage diii'erence between the 'condensers IO and 20 is 4zero when the trame density in the crossing streets is the same. In this situation an influencing of the free and blocked periods will not take place. The direction o! the voltage difference is dependent upon the voltages of the two condensers which operate on the grid Il, that is ltthe voltage of thel condenser 'i8 is greater or smaller than the voltage ofthe condenser 20. In one case it is termed as positive and in the other itis negative. The charging time of condenser 50 may vary between the upper and lower limit for the period during which the green or red signal is displayed. 'I'he charging time is further varied by the resistances 58 and 59. The object of the resistances 5B and 59 is to consider the different resistances 58 and 59 consequently are only required if the trame density in one of the crossingl streets is permanentlyl greater than in the other street.

` When'the condenser 50 has charged to the amount required, the glow tube or lamp 5l is ignited, the relay 52 is excited, the switch 63 is closed and the magnet 64, by means ot the pawland-ratchet mechanism and the switching drum,

vtraffic `densities in the crossing streets. The

throws over the switches 65 and 68 for yellow light, and the yellow lamp 61 shines.

The parallel connection of the switches 8 and ti which are controlled by the switch drum, and the manually operated switches 'I and 62 is provided with the object of operating the system until the yellow light appears, after the switches 'ly 'and B2 have been opened to put the signalling device out of action. When the signalling device is cut in again, it will at rst display yellow light. with the object aforesaid, the switches @and si are so designed that they automatically assume their active position for green" and red but are cut out for yellow by the switch drum, as will appear from Fig. 2. l

In order to obtain a constant period for the displaying ofthe yellowlamp 67, the switch 49 is closed at 49a during the yellow periodls, Fig. 2,`

and the resistances 58, 59 are short-circuited' thereby, so that the condenser 5l) is charged in aI correspondingly shorter time.

At the same time, the grid il of the valve 3d is connected to a negative voltage from the potentiometer di by the switch 34 closing the contact ich. When the switch 34 is at 3th, the diierence o1 the condenser voltages at it and 2li does not influence the grid' of valve .38, and, at the same time, further discharge of condenser 2t is prevented by the opening of dta, ilbfiiia. The condenser 2u ireeps the charge .it has at the moment the light changes to yello`w", and the charges produced by the vehicles arriving in the street about to be blocked, I

are added to the residual charge the condenser 20 lreeps.

From this moment, the residual charge, plus the charges produced by theV arriving vehicles, are preserved i'n the condenser til. 4"When, the signal changes to green the total charge of the condenser i6 for the blocked street is discharged through a resistance, and preferably through the.

same resistance 45.

Instead of providing the glow lamp J5I in the tilting oscillating circuit as described, for ing the condenser iii) under the thermionic valve or amplifier tube vide another amplifier tube to whose grid the voltage of condenser 5i) is connected, 'and whose anode current is controlled by this voltage.Vv The relay di, is ,in the, anode circuit oi this other amplifier tube. f

The operation of the tratiic in the blocked and tree streets upon the hereinbefore described syscontrol of the tem, to produce cyclic' changes ot,the stop caution' and go signals with periods of ston'and go auto-2 matically variablein response to tramo densities in the two streets, is substantially the same as'in the system described inmy co-pending application Serial No. 667,868 led April 25, ^1933.- That chargit, I may pro-A and 1d with the aid ofthe switch 65. 66.

is the vehicles in the control area of the blocked street are counted and produce a corresponding number of current impulses at I. The vehicles in the control area of the free street are likewise counted land produce aecorresponding number of current impulses at 2. These two sets of impulses charge the condensers I6 and 20 according to a logarithmic law and at diierent rates as described, the resultant charges, coresponding to the ratio of the numbers of vehicles counted in the control areas of the two streets, being imposed on the amplifier 39 and condenser 4I.. The output voltage of this amplifier actuates the trigger circuit 4at intervals determined by the time required for this vltage to build up suiilciently to break down the gap of the glow tube 5I. The

' length of these'intervals is thus also a function of the ratio oftrafiic densities in the two streets. At each operation of the trigger circuit the relay 52 energizes the drive magnet 64 to advance the signalling device to display the next signal. Thus every vehicle arriving in the control area of the blocked street abbreviates the period of the stop signal and every vehicle passing through the control area of the free street lengthens the periody of the go signal or in other words every vehicle in both'streets exerts an influence on the signalling device favorable to the control of the actual condition of tralc ilow in both streets.

By the term traffic density appearing in the f specification is meant the number of vehicles which pass a certain point such as the street crossing during a definite unit of time, or in other words the number of vehicles passing over and operating the control switch B during a definite unit of time.

When the switch 49 contacts the contact 49a takes place by means of the' switches 30 and 3|.

The reversal of the lamps 61 to 69 takes place by means of the switch cylinder shown in Figs. 1c The drive for the switch cylinder takes place with the aidv of the magnet 64, the circuit of which is controlled by the contact 63.

The relay 52 of the switch 63 is provided in the 'circuit of the condenser 50 and the tube 5I. As soon as the condenser 50 has received a charge sufllcient to start the glowing of thelamp Blythe current will ow through the coil of the relay 52.

Thus the switch 63 will be closed. The coil 64 will be thus energized and the switch cylinder will be actuated so that `the lamps will change as to their. indication.

The condenser 50 is continuously charged by the device 53 by means of the resistance 55 and the valve 38. For the continuity of the charge two influences are essential, one that the resistance 5l or the resistance 59 or neither of these are in the circuit and second which tension or voltage is present between the grid 31 and the wire 40.

This tension is zero when the condensers I6 and 20 have the same potential. In thiscase the same changev is only dependent on whether the resistance 5l or 59 or neither one of these resistances are switched into the circuit. 'I'he latter takes place when the switch 49 is in contact with the contact 49a. In this position the quickest charging of the condenser 50 will take place for a short period of the showing of the yellow signal.

If the resistance 58 or 59 is switched in a very definite time element takes place' in order to charge the condenser 50 by means of the va1ve,38, provided that there is no difference in potential between the condensers I6 and 20. A difference in potential between the two condensers influences the charging time which takes into consideration as well a longer or a shorter period. This is entirely dependent upon whether the tension in the condenser 2U or in condenser I6 is greater than the two condensers which are connected with the Valve by the switches 30 and 3i. The condenser 20 as shown in Fig. le is connected to the cathode 40. The condenser I6 is connected to the grid 31. Tlze condenser 20 is so arranged that as shown by the position of the switch it is for a free street and the condenser I6 is for a stop street. If now the tension in the condenser I6 is changed-over to condenser 20 then there is a shorter charging timefof the condenser 50 and thus there is a change from red to green and from green to red which occurs during a quicker period of time.

If, however, the change-over takes place the condenser I6 will be connected to the cathode 40. If now there is an over-balance of the tension there is a greater time necessary for charging the condenser 50 and thus a lo'nger time is necessary to carry out the change-over.

The switch 2 belongs to that particular street which as shown for the specific connections is for a free street. Thus it is necessary for the con- 1 denser 20 to have a parallel resistance connected.

thereto in order that the individual changes can after a certain time, ow through a resistance. This is necessary since otherwise the vehicles in the free street must have an opportunity to clear the intersection. As shown in Fig. 1e the condenser 20 is connected in parallel to the resistance 45. f

The condenser I6 does not have a resistance connected to it in parallel since for a stop street there are no vehicles which would remain in the intersection. If, however, there is a change from green to red then the condenser I6 must be connected in parallel to a resistance and in contradistinction thereto the condenser 20 would not be connected to a resistance. A

The changeover froingreen to red does not follow immediately but there is a yellow period between the green and red. Referring to Fig. 1e and Fig. 2 it will be noted that the green light is energized and then follows they closing of the switch 63 and the next operation'of the switch drum by the coil 64 will .result in a changing of the contacts in the switches 30, 34, 3|, 49 and 51. At the same time a yellow light is energized by means of the'switches 95--66. When the yellow light is showing the condenser I6 is connected to the cathode 40 but it has as yet no connection with theresistance or 46 and thus there is as yet no discharge of the charge for the yellow light period. The condenser 2U hns as yet no connection with the grid 31 but it also has no further connection with the resistance 45.

The charging of the condenser is not influenced by a difference in the charge of the condensers 6I) and 20 during the yellow light period.

. The time limit oi the yellow light, that is thetime for the charging pf ihe condenser 50 is taken care of alone by the 'resistance of the valve and the Zilli resistance 55. The resistances 58 and '59 are not in the circuit with the valve.

If now after the yellow light period, a further operation of the switch drum takes place and therewith the showing of the red light, the switches 3d and 49 are actuated. The condenser 2d is connected with the grid 3l and at the same time thc resistance 4t is connected in parallel with the condenser i6. This position remains until the next change to a yellow light period.

During the green light period there follows the charging of the condenser till by means of the resistance 59 whereas `for a red light period this takes place in view of the resistance 5t, whereas as already explained during the yellow light period the changing takes place directly through the circuit til.

I claim:

l. An automatic trafila control system for interfering trailic lanes comprising a signalling device with go and stopsignals for the control of traffic on said lanes, means operating said device to eiect alternate changes of signals to said lanes periodically, means controlling the period between successive operations of the device operating means to cause said signalling devices to display signals for variable periods, a vehicleactuated control for thelane having the go signal. a vehicle actuated control for the lane having the stop signal, each control having means for producing electrical impulses in response to actuation by vehicles on the respective lanes, a pair of condansers one of which is assigned to the control for the lane having the go signal and the other to the control for the lane having the stop signal, means responsive to the impulses produced by the go lane control for charging its corresponding condenser With successive increments of charge corresponding in number to the impulses produced in its control, a similar means for the condenser corresponding to the stop signal lane, and means for operating the period controlling means to ap portion the period between said change of signals in dependence on the immediate resultant of the two sets of charges in said condensers during the particular period.

2. An automatic trafdc control system for interfering trafiic lanes comprising a signalling del vice with go and stop signals :tor the control of trailic on said lanes, means operating said device to eect alternate changes of signals to said lanes periodically, means controlling the'period between successive operations of the device operating means to cause said signalling devices to display signals for variable periods, a vehicle-actuated control for the lane having the go signal, a vehicle actuated control forthe lane having the stop signal, each control having means for producing electrical impulses in response to actuation by vehicles in the respective lanes, a pair of condensers one of which is assigned to the control for the lane having the go signal and the other to the control for the lane having the stop signal, means responsive to the impulses produced by the go lane control for charging its corresponding condensers with successive increments of charge decreasing by a logarithmic law and corresponding in number to the impulses produced in its control, a similar means for the condenser corresponding to the stop signal lane, and means for operating the period controlling means to apportion the periods between said changes of signals in dependence on the immediate resultant of the two sets of charges in said condensers during the particular period.

`3. An automatic traflic control system for interfering traiilc lanes comprising a signalling device with go and stop signals for the control of trailic on said lanes, means operating said device to eect alternate changes of signals'to said lanes periodically, means controlling the period between successive operations of the device operating means to cause said signalling devices to display signals for variable periods, a vehicle-actuated control for the lane having the go signal, a vehicle 'actuated control for the lane having the stop signal, each control having means for producing electrical impulses in response to actuation by vehicles on the respective lanes, a pair of condensers one of which is assigned to the control for the lane having the go signal and the other to the control for the lane having the stop Signal, means responsive to the impulses produced by the go lane control for charging the condenser with successive increments of partial charge decreasing by a logarithmic law and corresponding in number to the impulses produced in its control, a

similar means for the condenser corresponding to the stop signal lane, resistances connected one with each condenser and through which it is successively charged, a manually variable resistance in parallel with the charging resistance of the condenser assigned to the go lane, and means for operating the period controlling means to apportion the periods between said change of signals in dependence on'the immediate resultant oi the two sets of vcharges in said condensers during the particular period.

4. An automatic tramo control system according tolclaim l, in which a lealr resistance is provided connected across the condenser of the go lane control and adapted to gradually discharge the said condenser during the go signal period.

5. An automatic traffic control system according to claim l, in which a lealr. resistance is provided connected across the condenser of the free street control and adapted to gradually discharge the said condenser during the go signal period, and inwhich means are provided for cutting out said leak resistance when'the signal changes to.

stop.

6. An automatic trafdc control system for interferng tramo lanes comprising a signalling device with go and stop signals for the control of traftlc on said lanes, means operating said device to eect alternate changes of signals to said lanes periodically, means controlling the device operating means to cause said signalling devices to display signals for variable periods, a vehicleactuated control for the lane having the go sig-v nal, a vehicle actuated control for the lane havlng the stop signal, each control having means for producing electrical impulses in response to actuation by vehicles on the respective lanes, a pair of condensersv one of which is assigned to the control for the lane having ,the go signal and the other to the control for the lane having the stop signal, means responsive to the impulses produced by the go lane control for charging its corresponding condenser with successive increments of charge corresponding in number to the impulses produced in its control, a similar means for the condenser corresponding to the stop signal lane, and means for operating the second-mentioned means in dependence on the immediate resultant Cil of the twoV sets of charges in said condensers 

